This invention relates to apparatus for adjustably mounting a wheel assembly to a motorcycle sidecar and, in particular, to such an apparatus which comprises part of a sidecar wheel suspension system and is adjustable to alter both the sidecar wheel toe-in and offset positions.
The advantages including increased load-carrying capacity and improved stability that are provided by a sidecar when attached to a motorcycle to form a combined vehicle, as shown in FIG. 1 have long been enjoyed by motorcycle enthusiasts. The attachment of a sidecar does, however, create some handling difficulties for the motorcycle rider. These handling problems are primarily due to the fact that the combined vehicle, i.e., the motorcycle with the sidecar attached, is asymmetrical both aerodynamically and about its center of gravity. Because the center of gravity is located off to the side of the motorcycle, acceleration and deceleration forces, and gravity forces while the vehicle is moving on an incline, tend to make the vehicle turn to one side or the other. Because of the aerodynamic asymmetry, head-on wind forces likewise tend to make the vehicle turn in one direction or the other rather than continuing in a straight line when so directed. If these forces are not otherwise compensated for, the motorcycle rider himself must continuously apply steering forces in order to make the vehicle travel in a straight line.
These handling difficulties can be alleviated by appropriately directing and positioning the sidecar wheel relative to the motorcycle wheels. Directing the sidecar wheel slightly inward toward the motorcycle by an angular amount T, as illustrated in FIG. 1, reduces the tendency of the vehicle to turn toward the right. A sidecar wheel which is directed inward in this manner is commonly referred to as having toe-in. The handling characteristics of the vehicle may also be improved by positioning the sidecar wheel an appropriate distance C, FIG. 1, from the rear wheel of the motorcycle. This relative longitudinal position of the sidecar wheel relative to the motorcycle wheel is commonly referred to as the sidecar wheel offset position.
For a number of reasons it is desirable to provide means for adjusting one or the other of the toe-in and offset positions of the sidecar wheel. The optimum offset position and amount of toe-in depends upon a number of variable factors including driver weights, passenger weights, road conditions, motorcycle size and weight, etc. Accordingly, a number of different types of apparatus for making such adjustments have been provided.
In U.S. Pat. No. 1,459,387 of Yeats et al., a toe-in adjustment mechanism is shown in which the wheel assembly is carried by an elongate member that is pivotally secured to the frame, referred to as a floating axle. Another member which extends transversely across the sidecar frame is pivotally secured to the wheel-carrying end of the first member, and includes means for securing it in a selected lateral position corresponding to wheel toe-in position. However, no means are shown for adjusting the offset position of the wheel. An offset adjustment mechanism is shown in U.S. Pat. No. 1,633,279 of Scala. There a wheel axle assembly, which traverses the entire sidecar frame, is slidably mounted along the lengths of parallel frame members to different wheel offset positions. However, no means are provided for adjusting the toe-in of the sidecar wheel.
While each of these mechanisms apparently performs the function for which it is intended, none of them is completely satisfactory when viewed with regard to its simplicity, accessibility for adjustment or versatility. A sidecar wheel suspension system is needed for good handling characteristics and rider comfort, and neither the structure of Yeats et al nor that of Scala is readily adaptable for use in a sidecar having such a suspension system which allows the wheel to move relative to the sidecar frame in response to road shock forces. Further, with regard to Scala in particular, adjusting the wheel offset entails the movement of a plurality of parts and loosening and subsequently tightening a plurality of securing elements, some of which are not readily accessible. Moreover, desirably the wheel adjustment apparatus should be capable of providing both wheel toe-in and offset adjustment and not just one or the other, as in the mechanisms discussed above.